1. Field of the Invention
The present invention concerns a multi-cylinder steam turbine, having a high pressure partial turbine, a medium pressure partial turbine and at least one low pressure partial turbine, which low pressure partial turbines are designed with two casings each having one outer casing and one inner casing supported within the outer casing and displaceable relative to it, each also having two low pressure steam feed pipes connecting the medium pressure partial turbine to these inner casings, which low pressure steam feed pipes are fed through the outer casings of the low pressure partial turbines and seal, on these, the outer casing internal space against the atmosphere by means of sealing devices which permit a displacement, parallel to the shafting, of the low pressure steam feed pipes relative to the outer casing, the shafting being located axially in both directions on a thrust bearing arranged between the medium pressure partial turbine and the high pressure partial turbine.
2. Discussion of Background
In multi-cylinder turbines which, in addition to a high pressure partial turbine, have a medium pressure partial tubrine and at least one low pressure partial turbine, measures have to be provided to ensure that the minimum necessary axial clearance is retained during operation between adjacent rotor and stator rings. In turbines of this type, in which the partial turbines are designed as two-casing turbines with an inner casing and an outer casing, such measures generally consist of connecting elements between the inner casing of the medium pressure turbine and the inner casing of the subsequent low pressure turbine and between the inner casing of the latter and the inner casing of and further low pressure partisa turbine and so on, should even more low pressure partial turbines be present. Something in the nature of a bearing position is then arranged between the high pressure partial turbine, referred to for short as the "high pressure part" in what follows, and the medium pressure partial turbine, referred to in what follows as the "medium pressure part", as the location point from which the high pressure part and the medium pressure part, together with the subsequent low pressure parts, can expand unhindered in opposite directions.
A multi-cylinder turbine with such a concept for providing compensation for axial clearance changes due to thermal expansions is described in DE-PS 1,216,322 by Rateau. In this, a single-casing medium pressure part, which is displaced along with its turbine rotor by the thermal expansions, transfers these expansions via coupling rods, which penetrate the outer casing of the two-casing arrangement of the low pressure part to the inner casing, to which they are hinged. The shaft, together with the turbine rotor, is displaced by the same amount as the inner casing, together with its blading, because it has substantially the same temperature as the inner casing so that the axial clearances between the nozzle guide vane and rotor blade rings are retained at practically the same magnitude as in the cold condition. The location point of the shaft, from which--on the one hand--the medium pressure part and the inner casing of the low pressure parts coupled to it can expand and be displaced freely and--on the other hand--the high pressure part can expand and be displaced freely in the opposite direction, is positioned at a bearing position between the high pressure part and the medium pressure part.
In this arrangement, the seals at the penetration positions of the coupling rods through the outer casings of the low pressure parts are problematic. In the patent mentioned, corrugated tubes or bellows or stuffing boxes or the like are proposed but all of these represent a possible fault source.